Chrome and Safari default <svg> width and height to 'auto', which
expands the viewport to fit the pixels within. Safari doesn't, and
the viewport collapses to 0x0 unless explicitly expanded.
Firefox calculates the viewport's natural dimensions to be 16x18,
so I used those values.
Fixes#8
The width does nothing as far as I can tell, and the height makes
the clickable boxes much higher than they need to, overlapping with
the paragraph before the button in the footer.
